Fixed Cmake build.
Fixed Cmake build.

In a previous commit we renamed 'nvidia.cpp' to 'isolator.cpp' in
'src/slave/containerizer/mesos/isolators/gpu/', but forgot to update
the Cmake build with this rename.

Review: https://reviews.apache.org/r/49421/

verizonlabs/mesos,verizonlabs/mesos,Gilbert88/mesos,andschwa/mesos,chhsia0/mesos,jpeach/mesos,craimbert/mesos,zmalik/mesos,gsantovena/mesos,yuquanshan/customizedMesos,zmalik/mesos,abudnik/mesos,zmalik/mesos,abudnik/mesos,gsantovena/mesos,neilconway/mesos,verizonlabs/mesos,asamerh4/mesos,neilconway/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,asamerh4/mesos,asamerh4/mesos,neilconway/mesos,gsantovena/mesos,kaysoky/mesos,abudnik/mesos,verizonlabs/mesos,jpeach/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,andschwa/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,chhsia0/mesos,neilconway/mesos,kaysoky/mesos,kaysoky/mesos,asamerh4/mesos,andschwa/mesos,jpeach/mesos,jpeach/mesos,dforsyth/mesos,asamerh4/mesos,abudnik/mesos,neilconway/mesos,Gilbert88/mesos,jpeach/mesos,dforsyth/mesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,neilconway/mesos,kaysoky/mesos,chhsia0/mesos,asamerh4/mesos,zmalik/mesos,dforsyth/mesos,jpeach/mesos,andschwa/mesos,chhsia0/mesos,andschwa/mesos,craimbert/mesos,reneploetz/mesos,asamerh4/mesos,reneploetz/mesos,reneploetz/mesos,chhsia0/mesos,Aman-Jain-14/customizedMesos,gsantovena/mesos,reneploetz/mesos,craimbert/mesos,dforsyth/mesos,reneploetz/mesos,andschwa/mesos,neilconway/mesos,verizonlabs/mesos,yuquanshan/customizedMesos,abudnik/mesos,craimbert/mesos,chhsia0/mesos,Aman-Jain-14/customizedMesos,abudnik/mesos,zmalik/mesos,gsantovena/mesos,zmalik/mesos,verizonlabs/mesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,verizonlabs/mesos,reneploetz/mesos,andschwa/mesos,craimbert/mesos,yuquanshan/customizedMesos,reneploetz/mesos,dforsyth/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,abudnik/mesos,kaysoky/mesos,jpeach/mesos,chhsia0/mesos,craimbert/mesos,craimbert/mesos,dforsyth/mesos,Gilbert88/mesos,gsantovena/mesos,gsantovena/mesos,zmalik/mesos,Gilbert88/mesos